Welcome to this video on common digital audio file word lengths.

We have learnt how longer word lengths reduce quantisation errors but increases file size. Historically word length has been constrained by storage, DSP and network bandwidth considerations which helps explain why the CD format word length is 16-bit.

Today these constraints are no longer issues. Almost all recent computers can store, replay and process multiple tracks of 24-bit audio.

However, for the audience there are still good reasons to keep file size to a minimum and there are therefore a variety of common word lengths in use.

Caption - 8-bit word length

Due to improvements in cost effective electronic components, 8-bit digital audio is no longer widely used except on older generation devices such as games consoles, mobile phones and samplers. 8-bit word length in audio files produces a relatively poor dynamic range of only 48dB.

Caption - 12-bit word length

12-bit word length is not used much today either, although the DV video format does have an option for 4-channel 12-bit audio, in addition to standard 16-bit stereo encoding.

Caption - 16-bit word length

The audio CD format utilises a 16-bit word length. At the time of CD's invention this was considered the best compromise for cost effective DSP and storage. A second of CD quality stereo audio contains two digital audio streams. Each has a sample rate of 44.1kHz and a 16-bit word length. 16-bit word length in audio files produces a dynamic range of 96dB.

16-bit word lengths are not constrained to CD's and can be used for any suitable application including computer software, hardware samplers, portable recorders and video camcorders.

Caption - 24-bit word length

This is the most common word length used for audio multi-track and stereo recording, production and mixing today. 24-bit ensures that fidelity can be better maintained as audio is processed and edited. 24-bit word length in audio files produces a dynamic range of 144dB.

Both standard DVD and Blu-Ray video formats also have an option for uncompressed 24-bit PCM audio, although most films released on them will feature MPEG compressed audio.

24-bit audio is not commonly used for music distribution, streaming and play back, where 16-bit CDs and compressed formats such as MP3 dominate. Despite calls from some in the music and audio engineering communities to distribute audio at higher sample rates and longer word lengths, it has still not been established that listeners can hear a difference between 16-bit and 24-bit in typical listening environments.

Caption - 32-bit word length

Because 24-bit is widely considered adequate, 32-bit audio is not in common use in digital audio distribution and retail. However, as we know from our video on word length and quantisation it is common place for DAW software to carry out processing at 32-bit or even 64-bit word lengths.

Caption - Variable word length

Unlike sample rate, which once chosen does not vary for the duration of a digital audio file, word-length can be variable. MP3, ACC and MPEG2 video are examples of file formats that can be encoded with so-called Variable Bit Rate, or VBR. In simple terms, conversion software contains algorithms that can analyse an audio file and vary the word length according to the harmonic content of the wave. This means that only sections that require it are encoded with a long word length.

Caption - Thanks for watching

The script for this video, with accompanying images, can be found at projectstudiohandbook.com 

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